Water flip-back

The water flip-back scheme is usually incorporated in NMR pulse sequences to be applied on proteins to provide further sensitivity gain for labile NH groups avoiding saturation of the water magnetization ( 93JACS12593 , 94JMRA178-107 , and 95JMRB94-108 ). It has been usually incorporated in HSQC-like puse trains, during the zz-magnetization selection period, as a selective water excitation pulse followed by a defocusing gradient element.

Applications:

  • 2D 1H-15N HSQC experiment ( 93JACS12593 , 94JMRA178-107 , 95JMRB94-108 and 98JB279-11 ).
  • 2D ROESY experiment ( 97JMR93-129 )
  • 2D TOCSY experiment ( 95JMRB168-111 , 96JB213-8 , and 97JMR93-129 )
  • 2D NOESY experiment ( 95JB327-5 and 97JMR93-129 )
  • 3D 1H-15N NOESY-HMQC experiment ( 98JMR87-135 )
  • Water-selective 90 pulse preceding the basic HMQC pulse sequence (1H-15N FHMQC experiment). implementation in 3D NOESY-15-HMQC and 3D 15-HMQC-NOESY-15-HMQC experiments. ( 98JB279-11 )
  • 2D 1H-15N TROSY experiment ( 99JB77-13 ) in which the proton pulse phases are designed so that the water magnetization is flipped back to the +z axis before the WATERGATE scheme. Implementation in 3D 1H-15N NOESY-TROSY and 3D 1H-15N TOCSY-TROSY experiments.
    • As a general trend, a selective 270 self-refocusing gaussian-shaped pulse (applied on-resonance on the H2O signal) around 2.5 ms is used for water flip-back purposes. The BRUKER's SYNTAX is
  • 1H water flip-back pulse length: p11=2.5m
  • 1H water flip-back pulse power (sp1): to be calibrated
  • 1H water flip-back pulse shape: spnam1=gauss